Lonious
Master Mariner
From the Wikipedia article on the Spanish Treasure Fleet, specifically the section dealing with changes to the treasure fleet system introduced by the Bourbon kings after the War of Spanish Succession:It's entirely possible that Centurion was one of these. So "SP_Pinnace50" would work, and not be overpowered as a starting ship. Alternatively, "FleutWar2" is valid for "Colonial Powers", has 34 guns of 12lb, and with 204 crew it's tier 5, also not too overpowered for a starting ship.
The "Villanueva" model is supposed to depict the character from the PoTC films. That puts him into "Colonial Powers" period. You can, of course, choose any Spanish character (including "Villanueva"), change the start date to something in "Golden Age", and then use cheat mode to give yourself any ship you like, including a fast war galleon.
The 44 gun specification is from a game involving cardboard models and is not necessarily Villanueva's ship in "At the World's End". Anyway, the fast war galleon doesn't have 44 guns either.
Ask @Bartolomeu o Portugues, he's the author of this quest.
I did consider changing the name and appearance of the "Will Turner" and "Elizabeth Swann" characters if you're playing Will Turner, but their dialogs would also need to change and so would "Will Turner's House" where you meet them. Much easier simply to disable this quest if you're Will Turner.
Challenges for FreePlay mode are the point of the Trophy Quests:
Trophies in the Free Play mode
Or there are character-specific quests such as "The Natividad Incident" for Hornblower, or "A Family Story" and "A French Companion" for José Joaquím Almeida. And any FreePlay character is free to make up additional goals, such as achieving a specific rank - that's the main point of FreePlay, set your own objectives and try to achieve them.
I did have one idea for "Barbossa2". Barbossa kills Blackbeard in "On Stranger Tides", not by attacking his ship but by duelling him on land. So, remove character "Blackbeard". "Barbossa2" starts off by default as a privateer in the service of Britain. When you reach a high enough rank, a governor can tell you to go after Blackbeard. (Any governor, or specifically the one at Port Royale?) Blackbeard is placed on his usual spot, you go to Isla de Muerte and duel him, and when he dies you get a self-dialog matching Barbossa's speech as he claims Blackbeard's sword and ship. You then get the Queen Anne's Revenge. And at that point, you leave the service of Britain and become a pirate because that's when Barbossa rips up his LoM in the film.
Trophies - was this ever actually implemented?
Barbossa2 - what about going on with my initial idea of a ship to ship battle? Just dueling him in Isla de Muerta feels...I dunno...just too ordinary.
I think the best option is a ship to ship encounter, then perhaps set some sort of duel in the cabin by default if you board the QAR. That way you get to fight him both on sea and "land".